Minimus 7 Loudspeakers - Measurements

[Yodathedog]

What crossover?

The PZ-2.1?

They’re a pair of 40-2034s. The crossovers are stock.

 

[z-adamson]

Put together before soldering to see how it fits...

 

[z-adamson]

Soldered up, wired up...

 

[z-adamson]

So I am 1 down and 3 to go.

Initial impression is that sensitivity is down, and power handeling is up. Some amp power goes up in heat within the crossover components so the drivers see less power.

Secondly, the 1 that is done sounds more refined.

 

[Pete B]

I've been thinking that it would be nice to do the Minimus 77 but you guys
have figured out that the current mod works in the 77.

The Polk T-15 looks interesting discounted to $59 a pair new, but they need
mods since the on axis response is not good.
Anyone have a pair?
I'm curious as to the DC resistance at the terminals measured with an ohm
meter in order to figure out the woofer impedance. There are a few reviews
with measurements out there on the T-15.

 

[z-adamson]

I've been thinking that it would be nice to do the Minimus 77 but you guys
have figured out that the current mod works in the 77.

The Polk T-15 looks interesting discounted to $59 a pair new, but they need
mods since the on axis response is not good.
Anyone have a pair?
I'm curious as to the DC resistance at the terminals measured with an ohm
meter in order to figure out the woofer impedance. There are a few reviews
with measurements out there on the T-15.

Here is an idea....a new and improved Minimus 26. Would you have the means to develop an improved crossover network?

 

[3-Crows]

I've been thinking that it would be nice to do the Minimus 77 but you guys
have figured out that the current mod works in the 77.

The Polk T-15 looks interesting discounted to $59 a pair new, but they need
mods since the on axis response is not good.
Anyone have a pair?
I'm curious as to the DC resistance at the terminals measured with an ohm
meter in order to figure out the woofer impedance. There are a few reviews
with measurements out there on the T-15.

I have some, the T-15. I am not entirely smart enough to figure out how to mod them but the build quality is decent and the price is decent and the sound is not awful. What measurement you need exactly? Just across the terminals?

 

[Pete B]

I have some, the T-15. I am not entirely smart enough to figure out how to mod them but the build quality is decent and the price is decent and the sound is not awful. What measurement you need exactly? Just across the terminals?

Across the terminals with an ohm meter (zeroed first) please.

 

[3-Crows]

Across the terminals with an ohm meter (zeroed first) please.

If I do not post my findings here tomorrow by the evening please PM me to remind me. I just need to get a ladder to get to them and I WILL do it for you, just give me until the afternoon. I was going to switch them out for my faux-Bois so this is good reason to get them down.

 

[3-Crows]

Across the terminals with an ohm meter (zeroed first) please.

Using my antique digital Micronta multimeter, I get it flashing between 3.9 and 4.0 Ohms.

I wonder if that eBay kit I used in my Minimus 7s would work on these?

Polk claims these are 8 ohms nominal.

 

[Pete B]

Using my antique digital Micronta multimeter, I get it flashing between 3.9 and 4.0 Ohms.

I wonder if that eBay kit I used in my Minimus 7s would work on these?

Polk claims these are 8 ohms nominal.

Thanks very much! I was hoping for closer to 6 ohms since they are rated as 8 but
at least I know now that it really is a 4 ohm woofer. Many speakers cheat in this way
since they only dip to 5 ish ohms at a few frequencies.
Here are two reviews, one measures lower dips in impedance, I wonder if they changed
the design or if one of the systems was out of calibration?
This review shows dips to 5 ish ohms:
https://www.audioholics.com/bookshelf-speaker-reviews/polk-t15

This shows dips close to 4 ohms:
https://www.audiosciencereview.com/forum/index.php?threads/polk-t15-bookshelf-speaker-review.11720/

Thanks again for checking, you confirmed that these are closer to 4-5 ohms min.

 

[z-adamson]

Second set...40-2039b.....minimus 7w

A little different from 40-2039a

Differences are.....the a has rubber feet, b does not. The a has the "supposed" better tweeter. They have different binding posts, crossover parts and back plate....see pic.

The a to the left, b to the right.

The b model was in my perception, a cost cutter.

The only thing the b has going for it is rubber feet.

 

[z-adamson]

Pics of my resto-mod 40-2039b...

 

[z-adamson]

And the last of my min 7 speakers...

PROX7

Just a recap for these. Different drivers completely, as such, i wasn't sure how the new crossover would work with them. Plus.....nowhere to put it, nothing to mount it flush to....cast aluminum cabinet complicating everything.

So recap it is.....just a single 4.7uf....had to get creative mounting it. Zip-tied it to the port tube, ran extensions to the terminal posts.

 

[z-adamson]

And I am done with the minimus 7 speaker restorations for the foreseeable future.

I would love to come up with a min 26 crossover.........but I am detecting a lack of enthusiasm here....

 

[Stuart Pedaso]

Differences are.....the a has rubber feet, b does not.

A packet of self-adhesive rubber feet was included with every model of Minimus-7. It was the owner's choice whether to apply them or not.

For cast aluminium cabinets, two of the feet are slightly taller and intended for the front. That's because metal cabinets taper down slightly at the front. It would otherwise be very difficult to eject the casting from the die without a draft angle designed in. Taller feet under the front compensate for the taper, effectively leveling the speaker.

 

[taineasy]

**********

Mod Summary:

http://www.audiokarma.org/forums/showthread.php?p=3671070#post3671070

Before vs. After frequency response:

**********

Baseline, unopened:

Including woofer on-axis nearfield 1/8" in front of grille, -32 dB:

Compare to Murphy's results here:

http://murphyblaster.com/content.php?f=minimus.html

Uncanny...! :thmbsp:

Edit:

History of The Minimus 7 Family

Minimus 7, 1978 to 1993, Models 40-2030 Black, 40-2034 Silver, 40-2039 Wood, 40-2045 White
Pro 7, 1994 to 1996, Models 40-2066 Black, 40-2065 White
Pro 7AV, 1994 to 1998, Models 40-2048 Black, 40-2059 White
Pro X7, 1995 to 1998, Models 40-2071 Gray, 40-2076 White
Pro-X44AV, 1999 to 2000, Models 40-2080 Black, 40-2081 White

The tweeter design was changed in 1983. The name was changed from Realistic to Optimus in 1994.

http://www.angelfire.com/vt/audio/minimus.html

Anyone ever built bass stands for the minimus 7 similar to those used by SZABO on the Szabo 424? Looking to build some stand-enclosures to elevate the height of the 7's and add a little bottom to the overall sound. Was thinking something 24-28" tall and 8" x 8' width/depth. Maybe a 6" woofer loaded as acoustic suspension to bring the LF down a tad but primarily to lift the db. The 7 plays to 50hz but down a ton.

 

[cipriano]

For anybody who bought an ebay crossover kit - Could you tell me the name of the seller?

The only thing I can find on ebay is matched capacitors, but no full kits.

Thanks

EDIT - on hifiengine.com on the Minimus 7 page, one of the reviews states that the crossover upgrade for the micca mb42 works well in the Minimus 7. Any thoughts on that?

Crossover Upgrade for Micca MB42/MB42-C Speakers (MKIII) | Micca Store (miccatron.com)

EDIT #2! - I found the ebay seller I was looking for. His name was litekeys but he seems to have disappeared within the past year. I hope he is doing alright.

 

[Stuart Pedaso]

For anybody who bought an ebay crossover kit - Could you tell me the name of the seller?

That would be "litekeys."
[edit] Ah, you've found him. Yes, he has had a spate of none shipment feedback issues lately. Doesn't bode well, in these current times. I too hope he prevails from whatever challenges he might be dealing with.

EDIT - on hifiengine.com on the Minimus 7 page, one of the reviews states that the crossover upgrade for the micca mb42 works well in the Minimus 7. Any thoughts on that?

Interesting. Not much technical details of crossover upgrade or even of stock MB42 on miccatron's website. Would be nice to see a schematic. That would open the opportunity to build one for test and evaluation in a Minimus-7.

The hifiengine poster ("Txt") stresses how using this already assembled crossover is the "easiest solution" compared to other DIY options. Could be he is challenged by manual construction projects. Or just short on time.

Of course its performance can't be fairly rated without a live evaluation. Though it's hard to imagine odds that would favour it over PZ-2.x mods. These have become the world celebrated standard, purposely designed for Minimus-7 by gifted professionals, with extensive testing and documentation in this very thread (with continuing support and developments by Pete B!).

If someone on AK does try the Micca mod in Minimus-7, I hope they post results. This thread could be a good place to share it.

 

[rothwellaudio]

EDIT - on hifiengine.com on the Minimus 7 page, one of the reviews states that the crossover upgrade for the micca mb42 works well in the Minimus 7. Any thoughts on that?

I'd guess that the speaker in question has nothing in common with a Minimus 7 other than similar dimensions, and therefore it seems highly unlikely that a crossover designed for one would be ideal for the other.